Preliminary work has shown that nitric oxide can displace a ligated fluorophore from a Co(II) porphyrin, restoring its fluorescence. This behavior will be exploited in the synthesis of fluorescein-porphyrin conjugates as possible fluorescent sensors for nitric oxide. A modular synthetic approach will be taken, in order to easily vary the attributes of the sensor and optimize its properties. The short term aims are: to develop efficient syntheses of soluble porphyrins with a single linking site; to synthesize linkable fluorescein derivatives containing a Lewis basic site for metal binding; to study the effect of different linkage strategies on the sensing properties of the molecule. The long term goal is to develop a stable, sensitive, water-soluble sensor. Such a sensor will then be used to study the production, diffusion, and uptake of nitric oxide in biological systems. Nitric oxide plays crucial roles in vascular relaxation, inflammation, immune response, neuronal potentiation and possibly memory formation. A sensitive sensor for nitric oxide will be a powerful tool in the study of all these roles. The ability to observe non-synaptic neuronal communication and map neural networks would make a nitric oxide sensor especially useful in the neurosciences.